1. Technical Field
The disclosure relates to broadband filters.
2. Description of Related Art
Three-phase AC powers are frequently used in manufacturing and conducting applications due to their favorable power generation, electrical distribution, and electrical to mechanical energy conversion characteristics. However, when three-phase AC powers are powered on/off, noise may be generated and transmitted to conductive wires, resulting in interference with other devices, usually loads, connected thereto. Such noise often includes differential-mode noise generated between live wires and neutral wires and common-mode noise generated between live wires and ground wires and between neutral wires and ground wires. Thus, there is a need for filters between the three-phase AC powers and loads for suppressing noise.
FIG. 1 is a circuit diagram of a filter 10 including a live wire L, a neutral wire N, a ground wire G, a differential-mode filtering circuit 101, and a common-mode filtering circuit 102. The differential-mode filtering circuit 101 includes inductors L1′ and L2′ and a capacitor C1′. The common-mode filtering circuit 102 includes inductors L3′ and L4′ and capacitors C2′, C3′, and C4′.
The capacitor C1′ and the inductors L1′ and L2′ filter differential-mode noise over the live wire L and the neutral wire N. The capacitors C2′ and the inductors L3′ and L4′ filter common-mode noise over the live wire L and the neutral wire N. The capacitor C3′ and the inductor L3′ filter common-mode noise over the live wire L and the ground wire G. The capacitor C4′ and the inductor L4′ filter common-mode noise over the neutral wire N and the ground wire G.
In the filter 10, the differential-mode filtering circuit 101 and the common-mode filtering circuit 102 both use one capacitor and inductors for filtering. However, capacitors have different equivalent series inductance and different equivalent series resistance during using, which resulting in that capacitors for filtering low frequency noise cannot filter high frequency noise and capacitors for filtering high frequency noise cannot filter low frequency noise. Thus, the filter 10 cannot effectively filter noise with limited filtering bands.